Owen Tuck
@owen_t_tuck
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PhD Candidate in the Doudna Lab at UC Berkeley
Joined July 2020
How does Hachiman work, and what can it teach us about immunity? Our structural and functional characterization of the Hachiman defense system is online: https://t.co/5IaYbegXAK Thanks to co-lead @ben_a_adler, @Emy_nim & coauthors at @doudna_lab. @igisci @UCB_Chemistry @HHMINEWS
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Now online! Genome integrity sensing by the broad-spectrum Hachiman antiphage defense complex
cell.com
Hachiman is a nuclease-helicase complex that protects against bacteriophage infection by destroying both viral and host genomes.
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🦠🧬Our paper is live @CellCellPress: Genome integrity sensing by the broad-spectrum Hachiman antiphage defense complex https://t.co/id7uU1YRIe Through structural, genetic and microbiological approaches, we show that Hachiman degrades DNA… by sensing low integrity DNA.
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🚨 New preprint alert! I am excited to present a collaboration between the @doudna_lab and Zev Bryant lab, with co-first authors @Noor_AlSayyad and @kevin_wasko and me. Curious about what drives high-efficiency genome editing by Cas9? Let’s dive in!👇🧵 https://t.co/pvjXKhM2tP
biorxiv.org
RNA-guided CRISPR-Cas enzymes initiate programmable genome editing by recognizing a 20-base-pair DNA sequence adjacent to a short protospacer-adjacent motif (PAM). To uncover the molecular determin...
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I am excited to share that our paper “Rapid DNA unwinding accelerates genome editing by engineered CRISPR-Cas9” from @doudna_lab is out in @CellCellPress! https://t.co/rsf4BLjzyj
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Our paper on the biochemical understanding of an engineered Cas9 (by directed evolution) is officially out @CellCellPress. “Rapid DNA unwinding accelerates genome editing by engineered CRISPR-Cas9” https://t.co/vR5655oLUR Following our previous study on the development of an
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The 2024 symposium on the immune system of bacteria is over. Thank you everyone for the great science, discussions and vibes. See you next year in Paris on April 8th-10th 2025.
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I’m excited to share my preprint on how Kiwa is used by bacteria to defend against phage infection! Graphical abstract and thread below 👇👇👇 https://t.co/Ii98CmcNmq
biorxiv.org
Bacteria have evolved numerous defence systems to combat phage infection, but our understanding of the underlying mechanisms is limited beyond their antiviral function. Here, we provide mechanistic...
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Mechanism of the Hachiman immune system finally deciphered A beautiful study from the Doudna lab shows that Hachiman is a genome integrity sensor https://t.co/kQFCGkJ7T1 Congrats @doudna_lab and colleagues!
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My friend @ben_a_adler and I co-led this work. Huge thanks to collaborators @Emy_nim & @JoePogliano, as well as talented @berkeleyMCB students @arushilahiri13, Jason Hu, and Julia Zhou. We're indebted to Jennifer for her constant support. 14/14
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Beyond mechanistic insights into a fascinating immune system, we hope to highlight the diverse and integral functions of helicases in immunity. 13/14
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There are functional symmetries and phylogenetic relationships between HamB and the Ski2-like recombination helicase Hel308. Hel308 is only present in archaea and metazoans. Could the two be evolutionarily linked? 🤔12/14
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We propose Hachiman activates in response to abberant DNA states. DNA ends load into the helicase, triggering ATP hydrolysis and release of HamA. HamA chews up DNA, potentially amplifying the immune response by creating more sites for HamAB loading. 11/14
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In another cryo-EM structure, we visualized nuclease-dead HamAB binding intact DNA in an orthogonal mode. We imagine this 'sliding' or binding state enables the helicase to thread ssDNA lesions into the active site. 10/14
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But why is Hachiman so effective against diverse phages? The trigger must be central to phage infection. We show that direct DNA damage induced by a drug activates Hachiman in the absence of phage! This key insight implies HamAB recognizes DNA damage as a viral signature. 9/14
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Our collaborators @Emy_nim and @JoePogliano @ucsdbiosciences showed Hachiman in action. When infected with phage, HamB completely shreds both phage and host DNA, leaving behind "phantom cells" devoid of genomes. Infected cells sacrifice themselves in service of the colony. 🫡8/14
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In another surprise, we discovered HamB is a DNA helicase! A set of structures shows DNA entering the HamB active site. We resolved 'ratcheting' states that lead to large domain movements upon activation. This motion may release the HamA nuclease. 7/14
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The structure led us to identify an active site for the HamA DUF! HamA is a nuclease homologous to nucleases in Type IIS restriction modification systems. HamA insertions mediate binding to HamB. The HamAB complex cuts DNA in vitro. 6/14
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To get at the mechanism, we turned to cryo-EM. HamA and HamB form a heterodimeric complex, with HamA contacting an N-terminal helical bundle in HamB. 5/14
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We identified Hachiman loci in E. coli isolates. ECOR31 Hachiman had strong, broad-spectrum activity against diverse bacteriophages. 4/14
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